Done by visiting the exterior of a cave with a partner. Splitting from the partner, then returning to the cave's original entrance and using Escape Rope brings the player back to the exterior (not the entrance).

From there, going back into the cave will join the player with the partner, though not from the intended point (i.e. at the entrance). Then, the partner will follow the player in strange patterns - similarly to how Pikachu followed a player in Yellow's Glitch City or during the Hooked Dragonite trick.

Any practical use for this? I haven't played B/W or B2/W2, so I'm not familiar with any new game concepts that could be used in conjunction with this quirk.

When going through Reversal Mountain for the first time, if the player enters the dungeon from the left side, causing Bianca to follow them, then goes through the southernmost exit and comes back inside, returning to the start of the cave, but not leaving the mountain entirely, Bianca will ask to split up. The player will then move to the next screen, where if they then use either an Escape Rope or Dig they will exit back to the southernmost point. Returning to the main part of the cave will cause Bianca's dialogue box to appear, but for her to be out of sight. After walking around for a while she will eventually catch up, but may travel through walls in the process.

I haven't tried it myself though, and haven't tried many Generation V glitches, so I don't know what you can do with it.

Forgiveness is timeless, and moments we look back on humble the soul. Jesus said it best. You must be blind to see and must see to be blind metaphorically is said. I don't think there is one Messiah nor a definitive truth, because we find truths in relative moments. However, there may be unknowable truths and sometimes it feels we have got to embrace the mystery and what we don't know.